Internal-combustion airplane heater



H. J. DE N. M COLLUM INTERNAL-COMBUSTION AIRPLANE HEATER Filed Mal ch25, 1942 4 Sheets-Sheet 1 y l I 6 Aug. 12, 1947.

Aug. 12, 1947. H. J. DE N. M coLLuM INTERNAL-COMBUSTION AIRPLANE HEATER4 Sheets-Sheet 2 Filed March 25, 1942 wzz zzzrcazzaa 4 Sheets-Sheet 3 ZJJ H. J. DE N. MOCOLLUM INTERNAL-COMBUSTION AIRPLANE HEATER Filed March25, 1942 Aug. 12, 1947.

Aug Q12, 1947. v J. DE N. MpCOLLU 2,425,630

INTBRN AL-COIBUSTION AIRPLANE HEATER riled larch 25, 1942 lamas-sheet 4Patented Aug. 12, 1947 IN TERNAL-COMBUSTION AIRPLANE HEATER Henry J. DeN. McCollum, Chicago, Ill.; Thelma McCollum, executrix of said Henry J.De N. McCollum, deceased, assignor to Stewart-Warner Corporation,Chicago, 111., a corporation of Virginia Application March 25, 1942,Serial No. 436,090

8 Claims. 1

My invention relates generally to heating apparatus and moreparticularly to heating apparatus of the liquid fuel internal combustiontype adapted for use in airplanes.

An object of my invention is to provide an improved internal combustionheater that burns vaporized liquid fuel in an enclosed space, thatdelivers an amount of heat adequate for large airplanes, that is simplein construction, light, in weight, safe and reliable in operation, andwhich requires a minimum of attention.

A further object of the present invention is to provide an internalcombustion type airplane heater that is operable throughout a widealtitude range without supercharging means.

Still another object of the present invention is to provide an internalcombustion heater using liquid fuel in which the combustible mixture iskept within a comparatively small zone, under all conditions, thuspreventing burning of fuel elsewhere than in a combustion chamberprovided specifically for this purpose.

Yet another object of the present invention is to provide an internalcombustion heater of improved type in which a temporary failure of thefuel to ignite within the combustion chamber will not result in the heatexchanger becoming filled with a combustible mixture.

A further object is to provide an improved internal combustion heaterfor airplanes and the like which will deliver a large volume of airheated to a desired temperature under substantially all conditions ofairplane operation.

Yet another object of the present invention is to provide a novel andimproved arrangement for deicing the wings and control surfaces ofaircraft.

Yet another object of the present invention is to provide a novel andimproved internal combustion heater adapted for use in airplanes whichaccomplishes the above objectives and which requires no connection to anairplane engine induction system and no connection to other specificpressure producing means.

Still another object of the present invention is to provide an improvedheater of the above type in which the air to be heated is maintained ata positive pressure above the pressure existing interiorly of thecombustion chamber and related passages, thereby preventing the productsof combustion from mixing with the air being heated in the event ofleaks developing in the system.

Other objects will appear from the following description, referencebeing had to the accompanying drawings, in which a 1 Fig. 2 is avertical transverse sectional view taken in the direction of the arrowssubstantially along the line 22 of Fig. 1;

Fig. 3 is a vertical transverse sectional view taken in the direction ofthe arrows substantially along the line 33 of Fig. 1;

Fig. 4 is a somewhat diagrammatic longitudinal sectional view of aportion of an alternative form of heater embodying the presentinvention;

Fig. 5 is a diagrammatic representation of the heater shown in Fig. 4drawn to smaller scale and showing the disposition of the heater withinan airplane Wing;

Fig. 6 is a vertical transverse sectional view taken in the direction ofthe arrows substantially along the line 66 of Fig. 4;

Fig. 7 is a plan view of an airplane wing with the leading edge portionthereof shown in section, illustrating a deicing system embodyingfeatures of the present invention;

Fig. 8 is a view similar to Fig. 7 but illustrating an alternativedeicing system embodying features of the present invention;

Fig. 9 is a side view of an airplane empennage with a portion of thesurface thereof broken away to show a deicing system embodying thepresent invention incorporated therein; and

Fig. 10 is a generally vertical sectional view taken in the direction ofthe arrows substantially.

along the line l0l0 of Fig. 9. I

Fig. 11 and Fig. .12 are diagrammaticvv views illustrating one type ofaspirating means which may be considered as connected to the end ofcasing illustrated in Fig. 5.

In the past, most efforts to heat airplane cabins usually consistedessentially of a simple heat exchanger in which heat was transferredfrom the engine exhaust to the air to be heated, or in some instances,the airplane engine exhaust has been used to produce steam, the steam inturn being used to heat the air in the cabin. It will be appreciatedthat the first of these systems has the inherentfdisadvantage that anyfailure of the heat exchanger will permit engine exhaust gases,including carbon monoxide, to leak into the cabin fresh air inductionsystem and even though the presence of carbon monoxide within the cabinmay not be sufficient to produce insensibility, it nevertheless greatlyreduces the efficiency. of the airplane occupants. In all aircraft, andin milil tary aircraft especially, this danger is a, seriousdisadvantage since a moments inattention on the part of the crew may bedisastrous.

The second of these prior used systems overcomes the above mentioneddisadvantage, but is expensive to manufacture, requires complicated' andeasily dislocated control mechanism, and is heavy, thus reducing theuseful load of the airplane considerably. Both of these systems have I.

the inherent disadvantage that useful quantities of heat are producedonly when the engines are operating at a comparatively high poweroutput.

Thus, substantially no heat is produced while the airplane is gliding orotherwise maneuvering with the engine operating at a reduced throttlesetting The airplane heater of thepresent invention supplies an adequateamount of pure air heated to the proper temperature, and the quantityand carbureter 38 fed from a fuel supply, not shown but from which thefuel passes to the carbureter 38 through a pipe Q9. The balancedcarbureter has an outlet tube 42 located below the fuel surface whichleads to an orifice or jet as within a Venturi throat 46, while asimilar orifice 48 temperature is unaffected by the changes in theoperation of the airplane engine; furthenthese factors are affected onlyto a minor degree by the airplane speed. It require no complicatedcontrols, is extremely light in weight and the products ofcombustion'cannot leak into the cabin fresh air induction system, sincethe pressure maintained inthe combustion chamber and within theheatexchange system is less than that in the fresh air induction system,therefore, any leaks developing in the heat exchanger will result infresh air leaking into the heat exchanger and mixing with the productsof combustion, rather than in the products of combustion leakingoutwardly into thefresh air system.

In Fig. 1 of the drawings, I have shown the leading edge portion of anairplane wing indicated generally by the numeral 20. The airplane heateris housed within this wing and comprises a heater induction pipe 22having an opening 24, at the leading edge of the wing which faces theair stream. A ramming effect is, therefore, produced at the mouth of thepipe 22. This heater induction pipe extends inwardly a hort distance andthen curves at right angles and extends generally parallel tothe leadingedge of the, wing and is connected at its opposite end to a heatexchanger 26 having a plurality of heat exchange tubes 28. These tubesare equipped with heat radiating fins 30, and at their oppositeends areconnected to an exhaust pipe 32 which extends rearwardly through thewing and opens therebeneath in a rearward direction, so that air movingpast the opening produces an aspirating effect which maintain thepressure within the heat exchange tubes 28 below that of the surroundingatmosphere. 7 v

The heat exchange portion comprising the tubes 28 and fins 36 islocated'within a fresh air induction pipe 34 which also has its open endat the leading edge of the wing facing in the direction of flight sothat a ramming effect is produced. The fresh air pipe extends rearwardlyand encloses the heat exchanger previously mentioned, and has itsopposite end connected to the space to be heated in the cabin. Since theair within the cabin is maintained at substantially atmosphericpressure, or perhaps slightly thereabove, because of the ramming effectat the mouth of the tube 34, it will be appreciated that the heatexchange tubes 28 are surrounded by a pressure greater than that in theinterior of these tubes. Thus any leakage developing in these tubes willbe accompanied by a flow of air inwardly through the tube walls ratherthan outwardly. I

The heat producing portion of the apparatus,

indicated generally by the numeral 35, is located I somewhat smallerthan the pipe '22 within which within the Venturi faces in the directionof the inflowing air and i connected to a tube 5!! which leads. to the.carbureter 38 and is connected to the bowl thereof above the liquidlevel therein.

TheVenturi throat 45 is formed within a heater induction tube 52, whichat its outlet end is closed by a generally conical plug 54. This plugtends to cause the air flowing through the tube to move radiallyoutwardly through radial ports 5'6 formed by punching veins 58 inwardlyfrom the side walls of the tube, as may best be seen in Fig. 3. Thecombustible mixture flowing through these ports, therefore, has aswirling motion. as it passes outwardly into a surrounding cylindricalcombustion chamber 60. r

The combustion chamber in diameter is some? what greater than theinduction tube 52, but

made from a high-chromium nickel alloy, such I as Inconel, for instance.7

The fuel passing into the combustion chamber 60 is adapted to be ignitedby an electrical resistance wire igniter BB suitably secured in anigniter housing 68 threaded into the side wall of the combustionchamber. The igniter and housing are preferably of the construction morefully disclosed and claimed, in my prior Patent No. 2,191,178. Thisigniter is controlled by a bulb type thermostatlfl having its bulblocated in a position between the combustion chamber 66 and the heatexchanger 25, the thermostat being connected in a circuit including asource of electrical energy 12 and an on and off switch hi, Thus whenthe switch M is closed,'the resistance wire of the igniter will beenergizedproviding the bulb i0 is cool. After the combustible mixturehas been ignited, and an operating temperature has been reached, thethermostat 10 will open the circuit tothe igniter, thus deenergizing thelatter.

Since the claim within the combustion chamber may become extinguished, are-igniter i6 is provided for re-igniting the combustible mixture, thusmaking it unnecessary for the system to cool sufficiently to bring thethermostat. it! into operation to reenergize the igniter resistance wire66. This re-igniter, maybe of the type shown in my copending applicationSerial N 0. 410,039, filed September 8, l94l, for Liquid fuel combustionapparatusand' is comprised of a spirally coiled sheet 18, preferablyof anickel chromium "alloy, such as Inconel or Nichrome-V, for instance,either of which is highly resistant'to the. deteriorating effects of gthe hot produc,ts of combustion present in the combustion chamber. Thespirally coiled sheet 18 is located in a central position within thecombustion chamber (HI and maybe attached; directly to the end of theinduction tube 52 by welding its outer coil thereto. During combustionwithin the combustion chamber, the re-igniter coil is heated to a hightemperature, and in the event that the flame becomes extinguished,combustible mixture passing into the spirally shaped pocket between theconvolutions of the coil will become heated sufficiently to re-ignitethe mixture. The convolutions of the coil 18 should be so orientedrelativeto the swirling effect produced upon the combustible mixture bytheradial ports 56 that the inertia of the rotating gases will tend tocarry them inwardly between the convolutions of the coil.

Although it is not critical, the annular space between the outer wallsof the combustion chamber and the heater air induction pipe 22 is ofsuch size that approximately twice as much air flows through thisannular space as flows-through the combustion chamber. With thisarrangement, the combustible mixture or products of combustion passingfrom the combustion chamber will be quickly mixed with the fresh airflowing through the annular space 62. Any combustible mixture is,therefore, diluted below the lower critical limit at which it will burn.Therefore, combustion is impossible outside of the combustion chamberregardless of whether or not combustion takes place within thecombustion chamber. One important result brought about by this featureis that if the combustible mixture within the combustion chamber shouldnot become immediately ignited, or if combustion should fail for somereason, the unburned combustible mixture passing from the combustionchamber will have sufficient additional air added thereto, so thatsubsequent ignition of the combustible mixture within the combustionchamber will not cause an explosionor burning in the heat exchanger orexhaust pipe 32. The arrangement, therefore, provides an inherent safetyfactor which makes it impossible for burning to take place anywhereoutside of the combustion chamber.

An additional advantage of this construction is that the hot products ofcombustion from the combustion chamber are quickly diluted withadditional cool air, thus reducing the temperature and increasing thevolume of hot gases passing through the heat exchanger. The fact thatthe gases passing through the heat exchanger are thereby considerablytempered, makes it possible to make the heat exchanger of lighter metalsthan would otherwise be possible. It also makes it possible to form theheat exchanger of thinner metals since the tempered and diluted productsof combustion have less corrosive effect upon the heat exchanger thanwould more concentrated products of combustion at a higher temperature.

In Figs. 4, 5 and 6, I have shown a modification of the heaterillustrated in Fig. 1. This alternative form is extremely simple toconstruct and extremely light in weight. Its longitudinal dimension issomewhat greater than the embodiment shown in Fig. 1, but ininstallations where a sufficiently long space is available, it isgenerally to be preferred over the arrangement shown in Fig. 1, becauseof its greater lightness and simplicity.

The combustion apparatus may be identical with that shown in Fig. 1 and,therefore, no additional description of this mechanism is needed here.The combustion apparatus is surrounded by a pipe 80 imilar to the heaterair induction pipe 22. This pipe is of considerable length and may bemade of comparatively light gauge aluminum tubing. The major portion ofthis tubing beyond the exit end of the combustion chamber is providedwith longitudinally extending creases or corrugations 82, thus providingconsiderable heat exchange surface in an extremely simple manner. Thesecorrugations also greatly stiffen the tube and, therefore, have astructural advantage. The heat exchange tube, the length and size ofwhich will be determined very largely by the heating capacity of theheater, extends a considerable distance from the combustion chamber, andat its outer end is connected to an aspirating vent 83 which may, ifdesired, be located at the under surface of the wing near its trailingedge. As in the embodiment shown in Fig. 1, this aspirating vent shouldpreferably maintain the interior of the heat exchange tube belowatmospheric pressure.

An air intake pipe 84 has its inlet end at an opening 86 at the leadingedge of the wing or other forwardly facing aircraft surface, so as toprovide a ramming efiect within the pipe 84. This pipe axially surroundsthe tube including the heat exchange corrugations 82 for substantiallythe entire length of the corrugations. Near the outlet end of thecorrugated portion the pipe 84 is closed around the corrugations and isconnected to a hot air pipe 88 leading to the aircraft fuselage.

In this device, the ramming effect at the opening 86 forces airthereinto somewhat above atmospheric pressure. This air is divided sothat approximately twice as much flows around the combustion chamber 60inside the pipe 80 as flows through the induction tube 52. The gasmixture, therefore, passing into the corrugated heat exchange portion istoo lean to burn, regardless of whether or not combustion has takenplace within the combustion chamber 60. The annular space between thepipe 84 and the pipe 80 is such that approximately four and one-halftimes as much air flows through this annular space as flows through theinterior of the tube 89, including that which flows through theinduction tube 52. The above proportions are given as examples only, itbeing understood that they are not critical.

It will be seen that the alternative heater shown in. Figs. 4, 5 and 6is in general similar to that shown in Fig. 1. The heat exchangerhowever is different, and only one air intake openingis used instead oftwo. It will be seen further that the arrangement shown in Figs. 4, 5and 6 is extremely simple to fabricate and can be extremely light inweight inasmuch as, with the exception of the burner, it can beconstructed almost entirely of comparatively thin walled aluminumtubing. Like the apparatus shown in Fig. 1, the embodiment shown inFigs. 4, 5 and 6 is inherently incapable of supplying a combustiblemixture beyond the end of the combustion chamber, thus preventingburning within the corrugated tube 82. It will be appreciated furtherthat with the exception of the carbureter 38 and the thermostat l0,neither of these heaters requires any moving parts. Although in theinterest of simplicity of illustration it is not shown in Fig. 4, thecarbureter and jet arrangement and the thermostatically controlledheater energizing circuit shown in Fig. 1 will normally be used with theapparatus shown in Figs. 4, 5 and 6.

In modern high flying aircraft, particularly military. aircraft, greatdifficulty is experienced tube.

with mechanism located within the wings'becatise of the extremely lowtemperatures encountered. At these low temperatures machine guns andother apparatus having moving mechanism usually refuse to operate unlessheated. For this reason electric heaters are frequently included whereheat is needed within the wings. However, with a heater embodying thepresent invention, branch pipes can be connected to the main hot airpipe so as to divert a portion of the hot air to the machine guns andother mechanisgn that should desirably be heated. These branch pipeswill add extremely little to the weight of the aircraft and in someinstances will involve nothing more than the formation of a smallopening in the side wall of the main heater pipe opposite the device tobe heated.

In Fig. 7, I have shown an aircraft wing deicer embodying features ofthe present invention. This deicer comprises a tube 90 which extendssubstantiall the length of the wing in a position closely adjacent tothe leading edge. This tube may be tapered as Shown so that its diameteradjacent the fuselage is somewhat greater than its diameter at the wingtip. At the wing tip the end of this tube is closed, while the side wallof the tube facing th leading edge of the wing is provided with aplurality of perforations 92, so arranged that air flowing into the tube90 will be forced out through these perforations against the insideleading edge portion of the wing. The inner end of the tube 90 isconnected to a forwardly facing opening 94 in the leading edge of thewing so that a ramming effect will be produced at this opening to forceair into the Air, therefore, flows into the opening 94, into the tube90, out of the openings 92 against the leading edge of the wing, andthence rearwardly within the wingand passes outwardly through aplurality of vents 96 located in the lower surface of the wing andpointed in a rearward direction so that an aspirating effect is Iproduced at these vents.

Closely adjacent the opening 94, the inner portion of the tube 90 isconnected to the outlet end of an internal combustion heater burner 98,generally similar to the burner shown in Figs. 1 and 4. In general, theburner 98 includes a combustion chamber, an igniter in the side wallthereof, a re-igniter, an induction tube having fuel jets therein and abalanced carbureter, all of the type shown in Figs. 1 and 4. The inletend of this heater can be connected to an air ram, or if preferred, itcan be connected to the outlet end of a small blower I having an inletopening I02 near the inner end of the leading edge of the wing.

The operation of this deicer is as follows:

When the aircraft enters an icing zone and the ice begins to collectupon the leading edge of the wings, the pilot energizes the igniter inthe side wall of the heater and the motor which drives the blower I00.The blower forces air through the induction tube of the heater, thusforming a combustible mixture which burns within the combustion chamber.The hot products of combustion flow from the combustion chamber into thetube 90 near its inlet end and are quickly mixed with air flowing intothe opening 94. They are thus considerably diluted and reduced intemperature and the warm mixture thus produced passes into the tube 90and outwardly through the openings 92 into contact with the leading edgeof the wing. It thus quickly raises the temperature of the a leadingedge of the wing sufficiently to melt ice formed thereon, oralternatively it raises the temperature of the 'wing sufficiently sothat ice cannot be formed thereon. The hot 'air after this is advisablewill depend largely upon the fuel used and, therefore, the chemicalcomposition of the products of combustion, and upon the interiorstructure of thewing and the mechanism located therein. Under thosecircumstances where it is not desirable toper'niit these products ofcombustion to circulate freely within the'i'nterior of the wing, thealternative structure shown in Fig. 8 may be used. This is essentiallysimilar to the arrangement shownin Fig. 7, excepting that the tube '90is not perforated and is placed in intimate heat transfer relation tothe leading edge portion of the wing. It mayin fact serve as one of thewing leading edge structural members, if desired, The outer end of thistube is connected to a tail pipe I04 which extends rearwardly andexhausts the products of combustion directly to the atmosphere.- Withthis arrangement the products of combustion heat the tube whichtransfers its heat directly to the leading edge of the wing, while theproducts of combustion flow outwardly to the atmosphere without cominginto contact with the interior structure of the wing. I 1

Although not specifically shown in the drawings, it will be appreciatedthat instead of using an inlet opening94 leading to the tube 90 and aseparate inlet opening I02 and blower I00 for supplying air to theheater, the arrangement shown in Figs. 1 and 4; may be used, that is, asingle ramming opening can be used for supplying air to the tube 90; andthe heater can belocated within the tube 90 so as to receive a portionof the air passing inwardly through the opening 94.

Figs. 9 and '10 illustrate the invention shown in Figs. 7 and 8 adaptedfor use in deicing the tail surfaces of the aircraft. In thisarrangement the vertical stabilizer I06 of the aircraft has an openingI08 near its upper extremity facing in a forwardly direction, which actsas an air ram. Air flowing into the opening I08 passes downwardlythrough a tube 0 located adjacent the leading edge of the wing andprovided with forwardly faced perforations II 2, similar to those shownin Fig. 7. These perforations cause air flowing into the opening I08 tobe forced against the leading edge of the vertical stabilizer. The lowerend of the pipe H2 is connected to a transversely extending pipe II 4which is located within the horizontal stabilizer H6 in a positionclosely adjacent its leading edge. The tube II4 likewise is providedwith perforations II8 which force air into contact with the leading edge0 the horizontal stabilizer, I

The trailing edge of the horizontal stabilizer I I6 and the trailingedge of the vertical stabilizer I06 are provided with a plurality ofvents I20 which have an aspirating effect, and permit the air flowinginto the interior of the stabilizers to be exhausted to the atmosphere.An internal combustion heater I22 of the type shown in Figs. 1 and 4 islocated within the pipe IIO in .a position slightly below the openingI08. Thus air flowing into the opening "38 passes downwardly through theheater, thus producing a combustible mixture which burns within thecombustion chamber, while a portion of the cool air flows around theheater and dilutes the products of combustion before the gases passdownwardly and out of the openings I I2 and l I8.

Preferably, a battle 324 extends inside the vertical stabilizer from aposition at the top thereof, downwardly behind the tube Hi] to aposition below the heater I22, and thence forwardly to the leading edgeof the stabilizer. Just above the portion of the baflle in contact withthe leading edge of the stabilizer, the tube H9 is provided with anopening I26 somewhat larger than the perforations H2. Thus a portion ofthe heated air will pass outwardly through the opening I25 and will flowupwardly to the top of the vertical stabilizer and out of anaspi'rating'opening I28 at the upper end of the vertical stabilizer. Thereason for providing the bafile I24 and openings I25 and I28 is thatthis arrangement insures hot air circulating upwardly, so as to heat theportion of the fin above the heater I22, thus maintaining the entire finin an ice-free condition.

If desired, the arrangement shown in Figs. 9 and 10 can be modified inthe same manner-that the arrangement shown in Fig. '7 is modified in thealternative embodiment shown in Fig. 8. That is, the tubes H and I M canbe provided without perforations and can be placed directly in heattransfer relation with the leading edge surfaces of the vertical andhorizontal stabilizers. In. the event that this arrangement is used, theends of the tube H4 located within the horizontal stabilizer should beconnected to the atmosphere.

All of the heaters and defroste-rs I have shown and described depend fortheir normal operation upon movement of the aircraft, but if groundheating is desired, this can be accomplished by connecting the outlet ofa blower to the ram openings, thus providing the necessary air movementthrough the several systems.

While I have shown and described particular forms of my invention, itwill be apparent to those skilled in the art that numerous modificationsand variations may be made in the particular constructions disclosedwithout departing from the underlying principles of the invention, I,therefore, desire by the following claims to include within the scope ofmy invention all such variations and modifications by whichsubstantially the results of my invention may be obtained by the use ofsubstantially the same or equivalent means.

I claim:

1. An internal combustion airplane heater comprising a conduit, a casingwithin said conduit in spaced relation to the wall thereof, meanscomprising an air ram to produce a pressure differential within saidconduit and casing to cause a flow of air through said casing andbetweenthe casing and said conduit, means in said casing forming a combustionchamber spaced from the walls of said casing and opening into a mixingchamber, an induction tube connected to said combustion chamber, meansto produce a pressure differential through said induction tube andcombustion chamber, said combustion chamber having an outlet forproducts of combustion. emptying into said mixing chamber, means toproduce a combustible mixture for induction into said combustion chambenmeans to ignite said mixture within said combustion chamber, said mixingchamber adapted to receive air flowing 10 through said casin andproducts of combustion from said combustion chamber, and the air flowthrough said casing being discharged into said mixing chamber insufiicient quantity to dilute any combustible mixture flowing from saidcombustion chamber sufilciently to prevent subsequent combustionthereof.

2. The combination set forth in claim 1, in which the heater is locatedin the wing of the airplane, and in which the pressure differentialproducing means comprises a ram in the air stream at the leading edge ofthe wing and connected to an inlet opening in said casing, and anaspirating means in the air stream at the trailing edge of the wing andconnected to an outlet opening of said casing.

3. In. an internal combustion airplane heater locatedin the airplanewing, a ram constituted by an opening in the leading edge of said wing,a conduit connected to said ram and to the space to be heated, a longnarrow casing located within said conduit and having its inlet openingfacing in the direction of said ram, aspirating means connected to theopposite end of said casing, said aspirating means being constituted byan opening in the trailing edge of the wing, said casing near its inletend providing a housing for a combustion chamber, a combustion chamberhaving inlet and outlet openings located within said housing and spacedfrom the walls thereof, a portion of said casing adjacent the outletopening of said combustion chamber providing a mixing Chamber andsubstantially the entire remaining portion of said casing providing aheat exchange surface, .means to supply a combustible mixture to saidcombustion chamber, means to ignite said combustible mixture in saidcombustionchamber, said conduit being so proportioned in size and shaperelative to said casing that the major portion of 'the air entering saidram flows between said conduit and said casing, said combustion chamberand said casing being so proportioned in size and shape that a portionof the air passing through said casing bypasses said combustion chamberin sufficient quantity to dilute any combustible mixture flowing fromsaid combustion chamber enough to prevent subsequent combustion thereofand that under dynamic conditions the pressure within said casing isless than the pressure between said casing and said conduit.

4. The combination set forth in claim 3, in which the casing comprises alength of tubing of substantially full diameter throughout the portionforming the housing for the combustion chamber and the mixing chamberand in which the heat exchange portion is corrugated longitudinally toincrease its stiffness and, heat transfer area.

5. In an internal combustion airplane heater, a conduit connected at oneend to the space to be heated and at its opposite end to an air pressureproducing means, a long narrow casing located within said conduit andhaving its inlet opening facing in the direction of said pressureproducin means, suction producing means connected to the opposite end ofsaid casing, means for partially obstructing the inlet opening of saidcasing so that under dynamic conditions the pressure within said casingis less than the pressure between said casing and said conduit, meanswithin said casing to burn a combustible mixture, means to dilute saidcombustible mixture adjacent said burning means and to pass saidcombustible mixture through the remaining portion of said casing, and aportion of said casing intween said casing and said conduit.

11 eluding heat exchange means-totransfer heat from the interionof saidcasing to the space he- .6.'The combination set forth in claim 5, in

which the pressure pro-ducing.means comprises .a ram in the aircstreamconnected'to the inlet 7. ,An internal combustion heater comprising acasing located in the wing of an airplane, means including an air ram atthe leading edge of the wing and connected to an inlet opening insaidcasing to produce a pressure differential 12 from said combustionchamber and the lay-passed air, and said second. portion of air beingdischarged into-said'mixingchamber in suificient within said casing tocause a flow of air therethrough, a combustion chamber located withinsaidcasing, an induction tube connected to said combustion chamber, saidinduction tube having an inlet opening facing against the direction ofair flow through said casing, said combustion cham er ha n an. outlet op odu o comhustion located downstream from said induction tube in andfac g i h dire tion o air w thr u h said ca in means to rod e a com.-

tio chamb r, m ans to iezfi e'sai m u W t in aid combus ion chambe .saidc mbustion chamberbei so oriented within ai asin and ofsuc si e rel ti eto the s e o a d as n t at a po tion f the ir flowin th ugh sai casin wil b -d verted so; a to. l w in o sa d induct and ombustion hamber andhence b c 25 bustllole mixture for induction into said combus- I saideasin wh le ars n p ion of the 1 quantity toolilute any combustiblemixture flow from said eornbustion'charnber suflieiently to preventsubsequent r qmb tifln th a c sin having an outlet opening and suctionproducin means in the air stream connected to said outlet opening ofvsaid casing.

8, The combination. set forth in claim '7 and means forming an enclosurefor said casing and means to pass air to. be heated through saidenclosure inheat exchange relation to said casing.

.1]. D MQCOLLUM.

REFERENCES QI'ITED The following references are of record in the file ofthis patent:

V UNITED 'sTnT 's PATENTS Number Name Date 2,285,718 Isaacson June 9,1942 2,295,177 King sept, a, 1942 1,349,668 Good Aug. 17, 1920 2,192,688McCo1lum Mar. 5, 1940 1,938,625 Engels Dec. 12, 1933 617,482 Baetz Jan.10, 1899 2,156,101 Willett et a1, Apr. 25, 1939 2,196,828 Hess Apr. 9,1940 2,046,521 Mahafiey V V V July '7 1936 2,142,699 amen Jan. 3, 19392,187,506 Van Daam Jan. 16, 1940 2,225,775 Garrett 1; 24, 194 0 FQREIGNPATENTS Number Country Date' 261,232 7 Great Britain 'NOV. 18,1926

